A project has been proposed to study the structure and function of cathepsin D. Purified enzyme of porcine or bovine spleen will be used. The study will concentrate on two aspects. First, identification of active sites by using specific diazo and epoxide inactivators will be made. The amino acid sequence near the active sites will be determined. Second, partial primary structure of cathepsin D will be determined. It is hoped that a structural and mechanistic homology between cathepsin D and other acidic proteases (pepsin, gastricsin and rennin) will be revealed.